This invention relates to a useful triarylamine dimer derivative having amorphous phase (non-crystal phase) for a charge transport material of an electrophotographic photosensitive conductor and a hole transport material of an electroluminescence elemental device, its manufacturing method, and organic semiconductors that applies them.
With regard to the organic electrophotographic photosensitive conductor, the organic semiconductor such as the layer-built electrophotographic photosensitive conductor is widely used.
The layer-built electrophotographic photosensitive conductor is laminated with a charge generation layer including a charge generation material such as phthalocyanine-type compound that generates the charge by irradiation of light and a charge transport layer including a charge transport material that transports the charge to a surface of the conductor.
Various solid solutions, that the charge transport material is dissolved into a binder polymer, are used for the charge transport layer of the organic semiconductor.
It is necessary that the charge transport layer is formed to be uniform. If the charge transport material precipitates to be hardly uniform on the occasion of forming thereof, it causes white hole fogginess on the occasion of printing. Therefore it is desired that the charge transport material has sufficient solubility into a binder polymer solution.
The charge transport materials used for the organic electrophotographic photosensitive conductor are instanced with a triarylamine derivative, an oxazole derivative, an oxadiazole derivative, a pyrazoline derivative, a hydrazone derivative, a hydrazine derivative, a triazine derivative, a quinazoline derivative, a styryl-type derivative, a styryltriphenylamine derivative, a butadiene derivative, a carbazole derivative and a benzofuran derivative, etc.
Above all, the triarylamine dimer derivative has an excellent charge transport property, and is widely used for the charge transport material of the organic electrophotographic photosensitive conductor of a printer or a copy machine, and the hole transport material of the organic electroluminescence elemental device.
The usual triarylamine dimer derivatives are instanced with N,N′-diphenyl-N,N′-bis(1-naphthyl)-4,4′-diaminobiphenyl (alpha-NPD) represented by the following chemical formula [A],
N,N′-diphenyl-N,N′-ditolyl-4,4′-diaminobiphenyl (TPD) represented by the following chemical formula [B].

Particularly alpha-NPD is widely used for the hole transport material in a field of the organic electroluminescence. And it is known that alpha-NPD has the excellent charge transport property. It is difficult to form the layer thereof because of its very low solubility into a solvent or a resin. A vacuum deposition method and so on is indispensable. Therefore, alpha-NPD as the charge transport material is not put into a practical use in a field of the electrophotographic photosensitive conductor that is formed by applying of the layer as a general procedure.
On the other hand, it is known that TPD is used for the charge transport material of the electrophotographic photosensitive conductor. However TPD often causes problems of the insufficient solubility or the crystallization on the occasion of forming the layer as the sensitive conductor onto a drum.
Up to now for example, patents about the following improved triarylamine derivatives have been applied.
In Japanese Patent Provisional Publication No. 2003-21921, examples of N,N′-diphenyl-N,N′-bis(2-naphthyl)-4,4′-diaminobiphenyl (beta-NPD) derivative for the charge transport material in the field of the electrophotographic photosensitive conductor are described. An alkyl substitutional group especially the methyl group is introduced to the derivative in order to improve the solubility.
In Japanese Patent Provisional Publication No. 2003-89681, triphenylamine dimer (3,4-TPD) derivative represented by the following chemical formula [C]
is described. The derivative has its excellent electronic property because of having very little content of impurity (TPD analog). And the derivative has an excellent formation property of the layer because of a low crystallization property.
In Japanese Patent Provisional Publication No. 8-291115, a triphenylamine derivative represented by the following chemical formula [D]
(in the chemical formula [D], -A is 1-naphthyl group or 2-naphthyl group) is described. The derivative can form a thin layer without using a binder resin by itself because of keeping amorphous state, namely glass state at normal temperature. And the derivative is useful for amorphous electronic materials having heat resistance because of having glass transition point of 100 degrees Centigrade.
In Japanese Patent Provisional Publication No. 2001-335542, the derivative represented by the following chemical formula [E]
(in the chemical formula [E], -A is 1-naphthyl group or 2-naphthyl group), that the above-mentioned triphenylamine derivative (the chemical formula [D]) is substituted by methyl groups, is described. The derivative (the chemical formula [E]) is used for the hole transport material of the organic electroluminescence elemental device.
In Japanese Patent Provisional Publication No. 9-316038, a diamine derivative represented by the following chemical formula [F]
is described. The derivative is useful to the hole transport material used for the organic electroluminescence elemental device or the electrophotographic photosensitive conductor.
In Japanese Patent Provisional Publication No. 2003-146950, the bisphenyl cycrohexane derivative represented by the following chemical formula [G]
(in the chemical formula [G], -A is a substituted or a non-substituted aromatic hydrocarbon group, etc., —R is a hydrogen atom or an alkyl group, etc.) is described. The derivative has excellent heat resistance on the occasion of a vapor deposition process, high glass transition point, electronic stability and chemical stability.
In Japanese Patent Provisional Publication No. 2000-256276, a method of manufacturing the triarylamine dimer by Ullmann reaction, that polyethylene glycol or dialkyl ether or monoalkyl ether as a reaction accelerator is used instead of crown ether (for example, 18-crown-6), is described.
Moreover, in Japanese Patent Provisional Publication No. 2003-89681, the similar method of manufacturing the triarylamine dimer is described.
Particularly it is necessary that the charge transport layer of the electrophotographic photosensitive conductor is formed to be uniform. Generally, the prior improved triarylamine dimer derivatives are prepared by a purification procedure such as recrystallization to have the crystal phase. These derivatives cause still the insufficient solubility into the organic solvent, or the crystallization on the occasion of forming the layer as the sensitive conductor onto the drum. Therefore these derivatives cause the problem that the charge transport layer becomes hardly uniform.
Moreover when an aliphatic substitutional group is introduced to the triarylamine dimer derivative for increasing of the solubility into the organic solvent, the aliphatic substitutional group having a long alkyl group makes the charge transport property of the triarylamine dimer derivative decrease. And the triarylamine dimer derivative cannot acquire the sufficient properties on the occasion of using for the charge transport layer of the electrophotographic photosensitive conductor.